(i) Technical Field
The present invention relates to an optical waveguide and a method of manufacturing the same and, more particularly, to an optical waveguide having a positioning mark and a method of manufacturing the same.
(ii) Related Art
Various methods for manufacturing a polymer optical waveguide have been proposed in the related art including, for example:
(1) a method in which films are impregnated with a monomer and in which the films are combined with the refractive index of a core part varied by selectively exposing the same (selective polymerization method);
(2) a method in which a core layer and a clad layer are applied, and a clad part is thereafter formed using reactive ion etching (RIE method);
(3) a method in which an ultraviolet curable resin provided by doping a polymeric material with a photosensitive material is exposed and developed using photolithography (direct exposure method);
(4) a method utilizing injection molding; and
(5) a method in which a core layer and a clad layer are applied, and a core part is thereafter exposed to change the refractive index of the core part (photo-bleaching method).
According to the above-mentioned methods of manufacturing a polymer optical wave guide, in general, a cutting process is performed using a dicing saw to form optical end faces after forming a core layer and a clad layer. At this time, a positioning mark (alignment mark) or positioning line formed in the optical waveguide is used as an index for setting alignment of the direction of cutting with the dicing saw or indicating the position to start cutting. An alignment mark is also used as a reference for positioning when an optical waveguide is optically coupled with another optical component. Referring to methods for such positioning, for example, an optical waveguide is optically coupled with an optical device such as a laser diode or photo-diode using techniques such as active aligning in which alignment is achieved by actually passing light between the elements and passive aligning in which alignment is alternatively be achieved using coordinates based on a positioning mark.
In general, a polymer optical waveguide of this type is restricted in that a refractive index difference between the clad and core cannot be great in order to optimize NA (a constant determined by the refractive indices of the core and the clad) which determines light propagation characteristics of the optical waveguide. For this reason, it is difficult to make a visual check on the amount and direction of any positional deviation of an alignment mark or positioning line to be used at the step of dicing an optical end face. As a result, the problem of difficulty in checking an alignment line mark or positioning line frequently arises during dicing not only when observing it with naked eyes but also when observing the alignment mark or the like with an existing image magnification apparatus. An alignment mark is also difficult to check with naked eyes when passive aligning is performed using coordinates, which results in an increase in the number of steps (time) of processing and consequently in a significant increase in manufacturing cost. The causes of such a problem include, for example, a small difference between the refractive indices of an alignment mark and a clad or core surrounding the same.